This specification pertains to new and improved castors which are primarily intended for use with so-called "pile carpet" but which are capable of being utilized in other applications.
The term "pile carpet" is commonly employed to designate a heavy fabric or fabric type structure for use in covering a floor or similar surface which is constructed so as to include surface fibers projecting upwardly from the principal portion of such a covering. These upwardly extending fibers are frequently referred to as the "pile" of the carpet. They may be either cut off so as to extend upwardly as more or less cantilevered beams or they may be upwardly extending loops of a continuous fiber.
In the past it has been recognized that when the pile on a carpet is held under compression as, for example, under a conventional cylindrical castor roller, for a prolonged period that such pile will tend to be distorted so as to "matt" downwardly from a normal position so as to lie roughly parallel to the principal portion of the carpet. To a large extent, this is a result of weight being concentrated on the wheel of a castor so as to be transmitted to only a limited portion of the surface of a carpet. It has also been recognized that it is possible to minimize such matting of pile carpet to various extents through the use of various expedients.
Obviously, the more the weight applied to the carpet through a castor wheel or roller is spread through a large area, the less the tendency for the carpet to matt under such a roller. It has also, however, been recognized that it is more desirable to prevent carpet matting by utilizing a roller of comparatively large length having a plurality of non-pointed bosses which will engage the pile of a carpet in such a manner as to "break up" the load applied to the carpet. The use of such bosses is considered desirable because to a certain extent such bosses tend to fit against the fibers of the pile on a carpet in such a manner as to spread the load so as to minimize matting and in such a manner as to tend to prevent a pile carpet surface from being uniformly compressed.
Although comparatively long rollers provided with such bosses are quite desirable and utilitarian, a problem has been encountered in connection with them. This problem concerns the turning or rotation of a castor about a vertically oriented axis. During such rotation the two different ends of a comparatively elongated roller turn different amounts. The bosses on a comparatively elongated roller type castor wheel have been found to tend to impede the rotation of a castor about a vertically oriented axis. This problem is more pronounced than with a roller having a completely smooth exterior surface because a smooth surface will tend to slip relative to carpet more easily than a wheel having exterior projections or bosses tending to fit downwardly within the fibers of the pile of a carpet.
It has been believed that it would be possible to remedy this problem by utilizing a series of comparatively thick, separate wheels, each of which is provided with a series of surface projections, mounted in such a manner that the wheels would rotate independently of one another. It is considered that this type of expedient is disadvantageous from a practical standpoint because of the possibility of the fibers within a carpet pile entering the space between the wheel and tending to "bind up" between adjacent wheels in such a manner as to effectively prevent or preclude rotation of the wheels. Further, it is considered that with this type of structure that there is danger of the pile within a carpet being damaged as a result of relative movement between the wheels at different rates as, for example, when a castor is turned about a vertically oriented axis.